Campbell CM 21, Инструкция по эксплуатации

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The irradiance at position 1 (pyranometer 'a') may be slightly different from
that at position 2 (pyranometer 'b') due to asymmetry in the lamp optics etc.
Therefore the pyranometers are interchanged and the whole procedure is
repeated. We get another pair of values: A' and B'.
6.3.3 Calculation
The sensitivity of the unknown pyranometer is calculated with the formula 2:
s S
b a
B B
A A
⋅
+
+
=
'
'
(formula 2)
S
b
= Sensitivity of the standard pyranometer at 20 ºC.
A = Output of pyranometer at position 1
A’ = Output of pyranometer at position 2
B = Output of standard pyranometer at position 2
B’ = Output of standard pyranometer at position 1
S
a
= Sensitivity of the pyranometer at 20 ºC.
Output = (mean value at 100% response minus zero offset signal)
6.3.4 Zero offset
The lamp housing and diaphragms are emitting long wave infrared radiation,
which heats up the outer glass dome and also, indirectly, the inner dome.
When the pyranometers are shaded, there still remains a small signal up to
+ 20 µV due to longwave infrared radiation from the inner dome to the
sensor. This zero offset is decreasing with a time constant (1/e) of several
minutes.
A zero offset was also embodied in the response due to illumination. To
correct for this unwanted response, the zero offset read after 30+30 s
shading is subtracted.